1. Technical Field
The present invention relates to semiconductor technology, and more particularly, to a variable resistive memory device and a method of manufacturing the same.
2. Related Art
As the demand for portable digital application devices such as digital cameras, MP3 players, personal digital assistants (PDAs), and portable phones increases, the market for nonvolatile memories is rapidly expanding. While flash memory devices are exemplary programmable nonvolatile memory devices, they are reaching their physical limits in terms of scaling. Thus, other nonvolatile memory devices such as phase-change random access memory (PcRAM) devices or resistive random access memory (ReRAM) devices using a variable resistor of which a resistance value is reversibly changed are being developed as alternatives to the flash memory devices. Since such nonvolatile memory devices use, for example, a resistance value change of the variable resistor to store a data state, a configuration of a cell becomes simple and thus miniaturization of the memory device becomes easier.
More specifically, PcRAM devices include memory cells that each include a phase-change material layer, which is reversibly switchable between a crystalline state having a low resistance value (referred to as a SET state) and an amorphous state having a relatively high resistance value (referred to as a RESET state). PcRAM devices operating as variable resistive memory devices may be realized by assigning logic values to different resistive states and reading out a resistance difference of each memory cell.
Currently, a germanium-antimony-tellurium (Ge—Sb—Te)-based alloy, which is a chalcogenide compound (for example, a Ge2Sb2Te5 alloy), has been developed as a phase-change material. Since the Ge—Sb—Te-based material has advantages of fast and stable phase-change and good oxidation resistance, the Ge—Sb—Te-based material is suitable for the PcRAM devices. However, since the Ge—Sb—Te-based material has only two kinds of resistance values corresponding to a set state and a reset state, one bit of data is stored in each cell. Thus, it is desirable to develop phase-change materials capable of storing 2 bits or more per cell and increase recording capacity of the variable resistive memory device.